Special plugs which may be part of a plugging head may be used for repairing pipelines or pipes which may conduct pressurized media such as oil, gas or even water. The plugging head is part of a hot-tapping equipment for repairing pressurized pipelines, for example. Hot tapping means drilling in a pressurized state and is a method adapted for drilling a hole in a pressure-conducting body and for forming a branching or bypass or bypass line in case of pipe portions which have to be repaired or even replaced. The hot-tapping process is carried out without operational interruptions and without leakage, providing the advantage that the pipeline operation can be maintained during repair works. In addition to the hot-tapping process (drilling under pressure), a line-stopping process has been commonly used. The line-stopping process is a method which enables a temporary interruption of a flow of media in a pipeline portion. Such an interruption of a flow of media through a pipe can be performed in case of repair, relocation and reconstruction works.
In case of equipment which may be used for performing the hot-tapping or line-stopping method, respectively, common elastomeric sealing disks are usually used, none of them, however, being able to fulfill the very specific process needs and requirements with 100 percent reliability. Examples for existing sealing principles come from companies such as IPSCO GmbH or T. D. Williamson, Inc., Tulsa, Okla. USA. T. D. Williamson Inc. of Tulsa, Okla., USA, for example, provides “stopple plugging machines” which are useful for maintaining the operation of a pipeline system during repair works. The TDW Inc. system known from bulletin No. 501.0 (Mar. 1, 1981) includes a hydraulic cylinder, a plugging head body, and a plugging head. A plurality of plugging heads of different sizes can be used together with this hydraulic cylinder. Typically, the “stopple plugging machine” from bulletin No. 501.0 of Mar. 1, 1981 is attached to a fitting which is flange-mounted to a tee of the pipeline. The body which accommodates the plugging head is flange-mounted thereon, and then, after application of a force to the hydraulic cylinder, the plugging head is introduced into the tee. The plugging head of the “stopple plugging machine” (cf. bulletin 501 of Mar. 1, 1981) has a lower end formed with a roll which abuts the lower part of the inner pipeline wall for aligning the plugging head during the further introducing movement which is essentially in a vertical direction, and for moving said plugging head into its sealing position. A sealing disk made of elastomeric material is mounted to the outer wall of the plugging head. When introducing the plugging head into the flow section to be sealed, it is reciprocated several times in order to “brush” the inner wall of the pipe or pipeline to remove deposits. As a result thereof, the sealing disk may be damaged to an extent where sealing becomes impossible. After moving the plugging head to its sealing position, the plugging head shuts off the pressure of the media prevailing within the pipeline. The flow directional pressure within the pipeline or pipe sealingly urges a sealing disk against the inner pipeline wall.
Meanwhile, it has been found that a very large radial gap between the plugging head (plug) and the inner pipeline wall of 20 mm or more cannot be sealed completely by using known approaches, and that process-reliability can therefore not be ensured. Considerably deformed cylindrical pipes of oval cross section cannot be sealed process-reliably by the annular sealing disk mounted to the plugging head, since it is in fact their oval shape which leaves relatively large gaps that cannot be bridged or sealed by a circular sealing disk. Moreover, it has been found that malleable sealing elements which have been used in known approaches are partly or completely undercut by the pressure to be shut off, and that it becomes impossible to dismount the whole sealing structure including the plugging head from the sealed flow section due to the constantly applied pressure which is to be shut off.